Rainbow Tusk is one of the three skins released in one part of the Rainbow Smashfest offer. It could be purchased as part of an item deal in late March 2021.
Rainbow Tusk could be purchased for $4.99 in a limited time deal which included a package of 6200 coins. It was not available for individual purchase and may not be available for purchase in the future.
Details of this skin can vary depending on location, platform or time.